1. Field of the Invention
This invention relates to a synchronizing signal generating circuit for timing the read-out or the recording when image read-out or recording is conducted by scanning a recording medium by a light beam emitted by a light source.
2. Description of the Prior Art
In image scanning read-out apparatuses for scanning a recording medium carrying an image stored therein by a light beam in a main scanning direction and in a sub-scanning direction, and detecting the image by use of a photodetector to obtain an image signal, read-out of the image signal is conducted, for example, by integrating the output of the photodetector for a predetermined time within the scanning period each time the position of the light beam is changed by a standard amount in the main scanning direction.
Also, in image scanning recording apparatuses for recording an image in a recording medium by scanning the recording medium by a light beam modulated with an image signal in a main scanning direction and in a sub-scanning direction, recording of the image is conducted, for example, by the modulated light beam each time the position of the light beam is changed by a standard amount in the main scanning direction.
In order to obtain a synchronizing signal when an image is read out or recorded as described above, a beam splitter has heretofore been inserted in the optical path between the means for scanning in the main scanning direction and the recording medium, thereby dividing the light beam into two light beams. One of the light beams thus divided by the beam splitter is used for image read-out or recording. The other is used for scanning on a grid for a position detecting monitor or for a linear encoder, and a signal generated as the scanning is conducted is shaped.
However, the conventional technique as described above has the drawback that, since many parts are required and the size of the apparatus becomes large, the apparatus is not easy to handle or to operate. Further, since the grid is expensive, a high manufacturing cost is required.
Also, in the conventional technique, since ambient dust accumulates on the surface of the grid, it is not always possible to obtain a consistent synchronizing signal.